Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

G:14 Glossary
germ cell A cell in the germ line of an organism, which
includes the haploid gametes and their specified diploid
precursor cells. Germ cells contribute to the formation of a new
generation of organisms and are distinct from somatic cells,
which form the body and leave no descendants.
germ layer One of the three primary tissue layers (endoderm,
mesoderm, and ectoderm) of an animal embryo. (Figure 21–3)
glial cell Supporting non-neural cell of the nervous system.
Includes oligodendrocytes and astrocytes in the vertebrate
central nervous system and Schwann cells in the peripheral
nervous system.
glycogen Polysaccharide composed exclusively of glucose
units. Used to store energy in animal cells. Large granules of
glycogen are especially abundant in liver and muscle cells.
(Figure 2–51 and Panel 2–4, pp. 96–97)
glycolipid Lipid molecule with a sugar residue or
oligosaccharide attached. (Panel 2–5, pp. 98–99)
glycolysis Ubiquitous metabolic pathway in the cytosol in
which sugars are incompletely degraded with production of
ATP. Literally, “sugar splitting.” (Figure 2–46 and Panel 2–8,
pp. 104–105)
glycoprotein Any protein with one or more saccharide or
oligosaccharide chains covalently linked to amino acid side
chains. Most secreted proteins and most proteins exposed on
the outer surface of the plasma membrane are glycoproteins.
glycosaminoglycan (GAG) Long, linear, highly charged
polysaccharide composed of a repeating pair of sugars, one of
which is always an amino sugar. Mainly found covalently linked
to a protein core in extracellular matrix proteoglycans. Examples
include chondroitin sulfate, hyaluronan, and heparin. (Figure
19–32)
glycosylphosphatidylinositol anchor (GPI anchor) Lipid
linkage by which some membrane proteins are bound to the
membrane. The protein is joined, via an oligosaccharide linker,
to a phosphatidylinositol anchor during its travel through the
endoplasmic reticulum. (Figure 12–52)
Golgi apparatus (Golgi complex) Complex organelle in
eukaryotic cells, centered on a stack of flattened, membraneenclosed
spaces, in which proteins and lipids transferred from
the endoplasmic reticulum are modified and sorted. It is the
site of synthesis of many cell wall polysaccharides in plants and
extracellular matrix glycosaminoglycans in animal cells. (Figure
13–26)
GPCR kinase (GRK) Member of a family of enzymes that
phosphorylates multiple serines and threonines on a GPCR to
produce receptor desensitization. (Figure 15–42)
G protein (trimeric GTP-binding protein) A trimeric GTPbinding
protein with intrinsic GTPase activity that couples
GPCRs to enzymes or ion channels in the plasma membrane.
(Table 15–3, p. 846)
G-protein-coupled receptor (GPCR) A seven-pass cellsurface
receptor that, when activated by its extracellular ligand,
activates a G protein, which in turn activates either an enzyme
or ion channel in the plasma membrane. (Figures 15–6 and
15–21)
G q Class of G protein that couples GPCRs to phospholipase
C-β to activate the inositol phospholipid signaling pathway.
Gram negative Description for bacteria that do not stain
with Gram stain as a result of having a thinner peptidoglycan
cell wall outside their inner (plasma) membrane, and on an
additional outer membrane.
Gram positive Description for bacteria that stain positive
with Gram stain due to a thick layer of peptidoglycan cell wall
outside their inner (plasma) membrane.
Gram staining A technique for classifying bacteria based on
differences in the structure of the bacterial cell wall and outer
surface.
granulocyte Category of white blood cell distinguished
by conspicuous cytoplasmic granules. Includes neutrophils,
basophils, and eosinophils. Arises from a granulocyte/
macrophage (GM) progenitor cell. (Figure 22–27)
granulocyte/macrophage (GM) progenitor cell Committed
progenitor cell in the bone marrow that gives rise to neutrophils
and macrophages. (Figure 22–31)
green fluorescent protein (GFP) Fluorescent protein
isolated from a jellyfish. Widely used as a marker in cell biology.
(Figure 9–24)
growth cone Migrating motile tip of a growing nerve cell axon
or dendrite. (Figure 21–72)
growth factor Extracellular signal protein that can stimulate a
cell to grow. They often have other functions as well, including
stimulating cells to survive or proliferate. Examples include
epidermal growth factor (EGF) and platelet-derived growth
factor (PDGF).
growth hormone (GH) Mammalian hormone secreted by
the pituitary gland into the bloodstream that stimulates growth
throughout the body.
GTP (guanosine 5′-triphosphate) Nucleoside triphosphate
produced by the phosphorylation of GDP (guanosine
diphosphate). Like ATP, it releases a large amount of free
energy on hydrolysis of its terminal phosphate group. Has a
special role in microtubule assembly, protein synthesis, and cell
signaling. (Figure 2–58)
GTP-binding protein Also called GTPase; an enzyme that
converts GTP to GDP.
GTPase An enzyme that converts GTP to GDP. GTPases
fall into two large families. Large trimeric G proteins are
composed of three different subunits and mainly couple GPCRs
to enzymes or ion channels in the plasma membrane. Small
monomeric GTP-binding proteins (also called monomeric
GTPases) consist of a single subunit and help relay signals
from many types of cell-surface receptors and have roles in
intracellular signaling pathways, regulating intracellular vesicle
trafficking, and signaling to the cytoskeleton. Both trimeric
G proteins and monomeric GTPases cycle between an active
GTP-bound form and an inactive GDP-bound form and
frequently act as molecular switches in intracellular signaling
pathways. See page 820.
GTPase-activating protein (GAP) Protein that binds to
a GTPase and inhibits it by stimulating its GTPase activity,
causing the enzyme to hydrolyze its bound GTP to GDP.
(Figure 15–8)
guanine nucleotide exchange factor (GEF) Protein that
binds to a GTPase and activates it by stimulating it to release its
tightly bound GDP, thereby allowing it to bind GTP in its place.
(Figure 15–8)
haplotype block Combination of alleles and DNA markers
that has been inherited in a large, linked block on one
chromosome of a homologous pair—undisturbed by genetic
recombination—across many generations.